the u.s. justice department announced this afternoon that it will join a civil lawsuit that claims armstrong defrauded the federal government. here's bob orr. >> reporter: the lawsuit as lance armstrong broke his sponsorship contract with the u.s. postal service by using performance-enhancing drugs while winning multiple tour de france titles. the postal service paid at least $31 million to sponsor armstrong's cycling team and now the justice department wants that money back and could seek total damages approaching $100 million. the lawsuit, first filed by armstrong's former teammate floyd landis in 2010, claims the team knowingly caused the united states postal service agreements to be violated by regularly employing banned substances and methods to enhance their performance. that charge brought strong denials from armstrong at the time. >> he's got no proof. it's his word versus ours. >> reporter: but in 2011, another teammate, tyler hamilon, told "60 minutes" armstrong did used banned subst